Which action indicates that the fifth wheel release handle is in the locked position?

The identification of the fifth wheel release handle being in the locked position is confirmed by the absence of space between the fifth wheel and the trailer apron. When the fifth wheel is properly locked, it should make direct contact with the trailer apron, ensuring a secure connection. This is vital for safety during operation, as any gap could indicate a potential disengagement or improper coupling, posing hazards on the road.

The other options, while they may reflect aspects of the overall equipment readiness or operational condition, do not specifically verify the locking status of the fifth wheel. For instance, operational trailer lights are important for visibility and signaling but do not indicate whether the fifth wheel is secured. Similarly, sealing air leaks contributes to the overall efficiency and safety of the braking system, but it is unrelated to the lock status of the fifth wheel. Lastly, while having the tractor engine running may be necessary for certain functionalities, it does not pertain to the mechanical status of the fifth wheel connection itself.